Internal heater for RF apertures

ABSTRACT

A heater for a radio frequency (RF) antenna and method for using the same are disclosed. In one embodiment, an antenna comprises a physical antenna aperture having an array of RF antenna elements; and a plurality of heating elements, each heating element being between pairs of RF elements of the array of RF elements.

PRIORITY

The present patent application claims priority to and incorporates by reference the corresponding provisional patent application Ser. No. 62/364,722, titled, “Internal Heater for RF Apertures,” filed on Jul. 20, 2016.

FIELD OF THE INVENTION

Embodiments of the present invention relate to the field of radio frequency (RF) apertures used for communication; more particularly, embodiments of the present invention relate to RF apertures, such as, for example, antennas, that include internal heaters.

BACKGROUND

Certain antenna technologies require heating of the antenna in order to bring the antenna to an operational temperature. For example, certain antennas that utilize liquid crystals must have the liquid crystals heated to a specific temperature in order for the liquid crystal to operate as desired.

In prior art related to liquid crystal displays (LCD), resistive heating elements are used to keep the LC above a specific temperature for proper operation, for example in automotive display applications where ambient temperatures can reach −30 C to −40 C. These heating elements are made from transparent conductors, such as Indium Tin Oxide (ITO) on a separate glass substrate from the primary LCD substrate. This substrate is subsequently bonded to the primary LCD substrate to provide thermal conductivity. Because the heating element is transparent to optical frequencies, this is a straightforward and practical way to implement a heater for LCDs, even though the heating element is in the signal path.

This approach, however, is not feasible when considering LC-based antennas. Because ITO and similar materials are not transparent at RF frequencies, placing these types of heater elements in the path of the RF signal will attenuate the RF signal and degrade the performance of the antenna.

Consequently, prior art embodiments of LC-based antennas use resistive heating elements attached to the metal feed structure or other bulk mechanical structures with good thermal properties to heat an internal portion of the antenna where the LC layer resides. However, because the resistive heating elements are physically separated from the LC layer by a number of layers in the antenna stack-up, including layers of thermal insulators, significantly more heat power must be applied in order to heat the liquid crystal, as compared to the LCD implementation.

Other implementations of LC-based antenna heaters attempt to heat the LC layer from the edges of the antenna aperture. These embodiments require 400-500 W of power and require 30-40 minutes at this power to bring the LC layer to operational temperatures. This is an inefficient use of heating power resources.

SUMMARY OF THE INVENTION

A heater for a radio frequency (RF) antenna and method for using the same are disclosed. In one embodiment, an antenna comprises a physical antenna aperture having an array of RF antenna elements; and a plurality of heating elements, each heating element being between pairs of RF elements of the array of RF elements.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will be understood more fully from the detailed description given below and from the accompanying drawings of various embodiments of the invention, which, however, should not be taken to limit the invention to the specific embodiments, but are for explanation and understanding only.

FIG. 1A illustrates heating wires with equal line lengths following gate and heater routing between RF elements.

FIG. 1B illustrates heating wires with unequal lengths on concentric arcs between RF elements.

FIGS. 2A-2C illustrate an example cross section of one embodiment of an antenna aperture.

FIG. 3A illustrates an example of a heater bus placement for heater wires of equal length.

FIG. 3B illustrates an example of heater bus placement for heater wires of unequal length.

FIG. 4A illustrates an example of heater buses crossing a border seal between layers in an antenna aperture.

FIG. 4B illustrates a generic cross section of a heater bus connecting to a heater wire inside an antenna aperture, extending under a seal and coming out to the bond pad structure on an iris layer overhang.

FIG. 5 illustrates a heater bus electrical crossover from an iris layer to a patch layer inside a border seal.

FIG. 6 illustrates a heater bus electrical cross over from an iris layer to a patch layer within a border seal structure.

FIGS. 7A-7C illustrate typical thin-film transistor (TFT) current (I)-voltage (V) curve at various temperatures.

FIG. 8A is a flow diagram of one embodiment of a process for determining an estimate of temperature of the LC using a TFT (or other type of transistor).

FIG. 8B is a circuit arrangement for measuring voltage and current for use in determining temperature within an antenna aperture.

FIG. 8C is a flow diagram of one embodiment of a process for determining an estimate of temperature of the LC using a TFT (or other type of transistor).

FIG. 8D is another circuit arrangement for measuring voltage and current for use in determining temperature within an antenna aperture.

FIG. 9 illustrates an arrangement for measuring capacitance of liquid crystal.

FIG. 10 illustrates an aperture having one or more arrays of antenna elements placed in concentric rings around an input feed of the cylindrically fed antenna.

FIG. 11 illustrates a perspective view of one row of antenna elements that includes a ground plane and a reconfigurable resonator layer.

FIG. 12 illustrates one embodiment of a tunable resonator/slot.

FIG. 13 illustrates a cross section view of one embodiment of a physical antenna aperture.

FIGS. 14A-D illustrate one embodiment of the different layers for creating the slotted array.

FIG. 15 illustrates a side view of one embodiment of a cylindrically fed antenna structure.

FIG. 16 illustrates another embodiment of the antenna system with an outgoing wave.

FIG. 17 illustrates one embodiment of the placement of matrix drive circuitry with respect to antenna elements.

FIG. 18 illustrates one embodiment of a TFT package.

FIG. 19 is a block diagram of an embodiment of a communication system having simultaneous transmit and receive paths.

FIG. 20 is a block diagram of another embodiment of a communication system having simultaneous transmit and receive paths.

FIG. 21 illustrates one embodiment of a superstrate having heating elements for heating inside an antenna aperture.

DETAILED DESCRIPTION OF THE PRESENT INVENTION

In the following description, numerous details are set forth to provide a more thorough explanation of the present invention. It will be apparent, however, to one skilled in the art, that the present invention may be practiced without these specific details. In other instances, well-known structures and devices are shown in block diagram form, rather than in detail, in order to avoid obscuring the present invention.

Embodiments of the invention include techniques for placing heaters (e.g., heating elements) on the interior of the liquid crystal cell of LC-based, radio frequency (RF) antenna apertures. In one embodiment, the heaters are placed inside the antenna aperture near the RF elements and closer to liquid crystal (LC) that is part of the RF antenna elements. This allows for more direct heating of the aperture, lessens the heater power requirements, and shortens the temperature rise time over techniques that use more indirect heating methods of raising the temperature inside the aperture, e.g., resistive heating elements on the back of the feed structure.

It is important that the heater implementation not interfere with the RF properties of the aperture. In one embodiment, the heater elements (e.g., heater traces) are located within the antenna aperture at locations that reduce, and potentially eliminate, RF interference while providing more direct heating within the aperture. In one embodiment, this is accomplished by putting heating elements between the RF elements on nearly the same plane as the RF elements. In one embodiment, the location of the heater elements is in the same plane as the iris elements of an iris layer that is part of a patch/iris slotted-array antenna. By moving the heater wiring inside the aperture onto nearly the same plane as the iris metal, the interaction of the heating wires with the RF signal is reduced, and potentially minimized.

The techniques disclosed herein also include methods for detecting the temperature within an antenna aperture. In one embodiment, the temperature is detected from a transistor directly on a transistor backplane. In one embodiment, the transistor backplane is a thin-film transistor (TFT) backplane. In one embodiment, if the transistors on the transistor backplane are in contact with an LC or other material, detecting the temperature of a transistor provides an indication of the temperature of the LC/material.

Techniques described herein decrease the cost of the heater system, require less power, decrease the rise time of the aperture temperature, and shrink the footprint of the controller board used to control the antenna. More specifically, in one embodiment, techniques described herein require 75-100 watts of power and will bring the LC layer temperature to operational temperature in 20 minutes.

Furthermore, temperature is typically sensed on the break-out printed circuit board (PCB), which is substantially physically removed from the glass assembly that includes patch and iris glass layers and an LC layer. On-glass temperature sensing provide much tighter control of the thermal management feedback loop.

Overview

In one embodiment, the heater structure consists of several parts: the heating elements, heater power buses to supply the heater elements, and connection schemes to connect the heater power buses to the heater power supplies that are located outside the aperture. In one embodiment, the heater elements are wires. In one embodiment, the heater power buses are of very low resistance.

The implementation of heater wiring, heater buses, and heater connections, depending upon implementation, may require additional depositions of conductor layers, passivation layers, via openings and so on during aperture fabrication. These additional layers may serve to build the heater structures, isolate the heater structure electrically or chemically from other structures, and to provide interfaces for the heater to existing aperture structure as needed.

Heating Wires

It is desirable that the heating of the aperture occur uniformly. Two configurations of heating wires are described herein that may achieve this objective.

In one embodiment, the heating wires are of equal length and the cross sections of these heating wires are the same (or similar) in dimension over the length of the heating wires and from heating wire to heating wire. In the aggregate, this provides the same power dissipation per unit area over the aperture. In one embodiment, the heating wires are evenly distributed over the aperture quality area, with heating wires laying between irises, not crossing or contacting the patches or irises. In one embodiment, the heating wires are close to the same distance apart from each other (the same pitch) across the aperture area.

FIG. 1A illustrates an example of heating elements used to heat the RF antenna elements in an antenna aperture, where the heating wires have equal line lengths and follow gate routing and heater routing between RF elements. In one embodiment, the gate routing is the routing to control gates that turn on and off liquid crystal-based RF antenna elements, which is described in more detail below.

Referring to FIG. 1A, an antenna aperture segment 100 illustrates one quarter of an antenna array of RF antenna elements. In one embodiment, four antenna aperture segments are coupled together to form an entire array. Note that other numbers of segments may be used to construct an entire antenna array. For example, in one embodiment, the segments are shaped such three segments coupled together form a circular array of RF antenna elements. For more information on the antenna segments and the manner in which they are coupled together, see U.S. Application Patent Publication No. US2016/0261042, entitled “ANTENNA ELEMENT PLACEMENT FOR A CYLINDRICAL FEED ANTENNA”, filed on Mar. 3, 2016 and see U.S. Application Patent Publication No. US2016/0261043, entitled “APERTURE SEGMENTATION OF A CYLINDRICAL FEED ANTENNA”, filed on Mar. 3, 2016. Note that the techniques described herein are not limited to operate with antenna aperture segments and may be used on single apertures that contain an entire array of RF antenna elements.

Heating wires (elements) 101 are shown on antenna aperture segment 100. In one embodiment, the heating wires 101 are equal in length. In one embodiment, heating wires 101 are located between RF antenna elements (not shown) in the antenna array. In one embodiment, heating wires 101 follow the gate lines used to control gates to turn on and off individual RF antenna elements in the array. In one embodiment, heating wires 101 are equal distance between the RF elements.

In one embodiment, heating wires 101 are equal distance with respect to each other. In other words, the separation between pairs of heating wires is equal. Note that this is not a requirement, though it may help with providing more uniform heating of the antenna aperture. In one embodiment, when the antenna elements in the antenna array are located in rings, individual heating wires in heating wires 101 are equal distance between two consecutive rings of RF antenna elements. In alternative embodiments, the separation between pairs of heating wires is not equal.

It should be noted that the heater wiring depicted in FIG. 1A indicates the relative position and routing of the wiring, but does not represent the wiring size or number of wires. For example, in one embodiment, every other wire may be removed with the remaining wires providing the necessary heating where the heating is provided uniformly over an area. With respect to the size of the heating wires, their size is based on the material properties of the heating wire itself and the amount of heating the wires are to provide.

In one embodiment, the heating wire cross section (height and width) of heating wires 101 is chosen in the following way. First, the required power for heating the aperture area is converted, for a given desired heater supply voltage with the number and length of the heating wires, to a resistance for the heating wires. In turn, this resistance value is used in conjunction with properties of the heating wire materials to determine the required heating wire cross section. Note that other considerations may be used to select the heating wire cross section, including, but not limited to fabrication yields.

In another embodiment, the heating wires are unequal in length and their cross sections are not equal. In one embodiment, where the heating wires with unequal lengths are on concentric arcs between RF elements. In one embodiment, the heater wire widths are equal and the wire heights are adjusted radially from the center of the segment to provide uniform power per unit area over the aperture area.

FIG. 1B illustrates an embodiment of the heating wire on an antenna aperture having heating wires of unequal length and their cross sections are unequal to each other. Referring to FIG. 1B, heating wires 111 are shown on antenna aperture segment 110, which is the same type of aperture segment as depicted in FIG. 1A. In one embodiment, a number of antenna apertures are coupled together to form a complete antenna array. As in FIG. 1A, in one embodiment, the heating wires are routed between the RF elements. In one embodiment, that routing follows the gate routing for the gates that control the antenna elements.

In one embodiment, an objective is still to provide nearly uniform power dissipation per unit area. In this case, however, the height of the heating wire cross sections are varied over the aperture area to control the current and resistance to provide the same power dissipation per area although the heating wires are of unequal length.

It should be noted that the heater wiring depicted in FIG. 1B indicates the relative position and routing of the wiring, but does not represent the wiring size or number of wires. With respect to the size of the heating wires, their size is based on the material properties of the heating wire itself and the amount of heating the wires are to provide.

In one embodiment, the heating wires lie between the iris features and do not cross or contact the patch or iris features in a tunable slotted array of antenna elements having patch/slot pairs. In the illustration examples provided in FIGS. 2A-2C, the heating wires lie in rings midway between the rings of iris/patch elements, with an additional inside and outside ring of heating wires. In one embodiment, the rings of heating wiring are on concentric rings at the same radial pitch over the aperture area. In one embodiment, the heater wiring radial pitch is the same radial pitch as the RF elements. In alternative embodiments, the heater wiring radial pitch is not the same as the radial pitch of the RF elements.

In one embodiment, the heater wires lie close to equidistant between the RF elements.

FIGS. 2A-2C illustrate an example cross section, or side view, of an antenna aperture having iris and patch layers. Referring to FIGS. 2A-2C, patch layer 201 and iris layer 202 are separated with respect to each other include patch and iris slots, respectively, to form a tunable slotted array. Such an array is well-known and is also described in more detail below. In one embodiment, patch layer 201 and iris layer 202 are glass substrates. Note that the patch layer and iris layer may be referred to below as a patch glass layer and an iris glass layer, respectively. However, it should be understood that for purposes herein, the embodiments that include “patch glass layer” and “iris glass layer” may be implemented with a “patch substrate layer” and an “iris substrate layer,” respectively, (or patch substrate and iris substrate) when the substrate is other than glass.

Patch metal 211 is fabricated onto patch glass layer 201. A passivation patch layer 231 is fabricated over patch metal layer 211. A liquid crystal (LC) alignment layer 213 is fabricated on top of passivation patch layer 231. Sections of iris metal layer 212 are fabricated onto iris glass layer 202. Passivation iris layer 232 is fabricated over the iris metal 212. Heating wire 240 is fabricated on top of passivation iris layer 232. In one embodiment, heating wire 240 is close to equal distance between a pair of iris elements. Other heating wires are also located between iris elements in this fashion. Another passivation layer 233 is fabricated over passivation layer 232 and heating wire 240. LC alignment layer 213 is fabricated on top of passivation iris layer 233.

Note that the LC alignment layer 213 is used to align the LC 260 so that it is pointing in a single direction in a manner well known in the art.

Heater Power Buses

Power buses are provided to supply power to the heating wires. Examples of these are illustrated in the figures below. In one embodiment, the power buses are of low resistance when compared to the heater wires, by several orders of magnitude, so that there is a small voltage drop from one end of the bus to the other, so that all of the heating wires may have the same voltage at each bus end of the heating wire. This makes it simpler to manage the power distribution to the network of heating wires.

In one embodiment, the heater buses are placed inside the aperture so that the heating wires are able to connect to the proper supply voltages at each end of the heating wire.

In one embodiment, the heater buses are separate structures placed into the apertures solely for the purpose of providing power to the heater wire network.

In another embodiment, existing structures in the aperture may be used to also act as heater buses. In one embodiment, the heater bus (or buses) are built into the seal structure of the aperture. In another case, the iris metal (e.g., copper) plane may be used as a heater bus to sink or source current for the heating wires.

FIG. 3A illustrates an example of heater power bus placement integrated on an antenna aperture for heater wires of equal length. Referring FIG. 3A, antenna aperture segment 300, which represents one of the antenna segments that are coupled together to form an entire antenna array, includes heater bus lines 301 and 302. Heater power bus lines 301 and 302 are electrically connected to and provide power to heating wires 303.

FIG. 3B illustrates an example of heater power bus placement integrated on an antenna aperture for heater wires of unequal length. Referring to FIG. 3B, heater power buses 303 and 304 are electrically connected to heating wires 305 on antenna aperture segment 310.

Heater Bus to Power Supply Connection

In one embodiment, heater buses on the inside of the aperture are brought outside of the aperture structure to make connection to the heater power supply. In one embodiment, this can be accomplished by connecting the heater buses through a border seal structure at the outer portion of the antenna aperture to a metallization layer on one of the layers in the aperture outside the aperture border seal. For example, one such metallization layer is on the iris glass layer or on the patch glass layer. This metallization connects to the heater buses inside the seal and extends from inside the seal, through the seal, and out to portions of the patch or iris glass layers that extend beyond each other. These may be referred to as overhang regions. In such cases, portions of the patch or iris glass layers beneath those overhang regions may be referred to as under-hang regions.

FIGS. 4A and 4B illustrate examples of the heater buses coming through the border seal out onto the iris glass layer overhang. In one embodiment, the RF aperture, in this case, is cut so that both the iris glass layer and the patch glass layer have overhang regions (where the substrate has a metallized region not faced by glass layer opposite the metallized face). Note that while the iris and patch layers may be described herein at times as glass layers, they are not limited to being glass and may constitute other types of substrates.

FIG. 4A illustrates a heater bus connection scheme for use in connecting the heater bus to a heater power supply. Referring to FIG. 4A, in one embodiment, the heater power supply (not shown) is located outside of the antenna element array, such as antenna element array 430, which includes the heating wires. Antenna aperture segment 400 includes a patched layer and an iris layer as discussed herein. A portion of the iris layer, referred to as iris overhang 401 and 402 extends over portions of the patch layer. Similarly, a portion of the patch glass layer, referred to herein as the patch overhang 403, extends beyond a part of the iris glass layer. The iris glass layer and the patch glass layer are sealed together with an aperture border seal 460. Heater power bus 410 crosses border seal 460 at seal crossing 421. Heater bus 411 crosses border seal 460 at seal crossing 420 and connects to a power supply. In both cases, heater power bus 410 and heater bus 411 are able to connect through a power supply by exiting antenna aperture segment 400. Antenna aperture segment 400 includes heater power buses 410 and 411 electrically connected to heating wires 481 in the antenna element array 430.

FIG. 4B is a generic cross section of a heater bus connecting to a heater wire inside the aperture, extending under the seal and coming out to the bond pad structure on the iris overhang. Referring to FIG. 4B, heater bus metal 443 goes under a border seal, border seal adhesive 450, on the iris glass layer 431 on top of passivation layer 446. Thus, heater bus layer 443 is underneath border seal adhesive 450. Border seal adhesive 450 couples the patch layer 430 to iris glass layer 431 including the fabricated layers thereon.

Heating wire 444 is deposited on top of passivation layer 446 and a portion of heater bus metal 443, thereby electrically connecting to power bus metal 443 with heater wire 444. Heater wire 444 is fabricated on a portion of passivation layer 441 that is fabricated on top of iris metal 445 and is fabricated onto a portion of heater bus metal 443. In an alternative embodiment, there is a passivation layer between heater bus metal 443 and heating wire 444 with a via through the passivation layer connecting heater bus metal 443 and heating wire 444.

Passivation layer 441 is fabricated on top of heating wire 444 and at least a portion of heater power bus metal 443. An alignment layer 432 is fabricated on top of passivation layer 441. Passivation layer 441 is also fabricated on the bottom of the patch layer 430. Similarly, alignment layer 432 is fabricated over a portion of passivation layer 441 on the patch layer 430. Note that while heater wire 444 is shown deposited directly on top of heater bus metal 443 without a passivation layer and via in between, in an alternative embodiment, another layer of passivation is deposited between heater wire 444 and heater bus metal 443 with an electrical connection between the two being made using a via. This layer of passivation protects the heater bus metal while the heater wire metal is being etched.

Bond pad/connector structure 442 is a location to electrically connect the power supply to heater bus metal 443.

The power for the heater buses may cross from the patch glass layer side of the aperture to the iris glass layer side of the aperture inside of the border seal, within the border seal itself, or outside of the border seal. Bringing the heater buses out to the patch layer overhang has the advantage of possibly making the heater connection within the connector used for the rest of the interface lines from the controller electronics to the aperture. The following illustrations show methods of doing this inside and within the border seal.

FIG. 5 illustrates on embodiment of a heater power bus electrically crossing over from iris layer to the patch layer inside a border seal. Referring to FIG. 5, patch glass layer 501 is shown over iris glass layer 502. There are a number of layers fabricated onto patch glass layer 501 and iris glass layer 502 and a border seal adhesive 521 couples these two substrates together. In one embodiment, patch glass layer 501 and iris glass layer 502 comprise glass layers, though they may be other types of substrates.

Iris metal layer 541 is fabricated on top of iris layer 502. Passivation layer 531 is fabricated on top of iris metal 541 and the iris layer 502 where iris metal 541 is absent. Over passivation layer 531 comprises heater bus metal 512. Over the passivation layer 531 that is over iris metal 541 is passivation layer 550. Heating wire 510 is fabricated on top of passivation layer 550 and on top of a portion of heater bus metal 512. In an alternative embodiment, there is a passivation layer between heater bus metal 512 and heating wire 510 with a via through the passivation layer connecting heater bus metal 512 and heating wire 510. Passivation layer 530 is fabricated over heating wire 510 or at least a portion of heating wire 510, with alignment layer 540 on top of passivation layer 530. On patch layer 501, a passivation layer 532 is fabricated. On top of passivation layer 532 is a metallization 511 supplying the heater bus. A passivation layer 530 covers a portion of heater bus metal 511, while alignment layer 540 covers a portion of passivation layers 530 and is used for aligning LC 560. A bond/connector structure 513 is located to allow an electrical connection between the heater power bus and an external power supply (not shown).

Conductive cross-over 520 electrically connects the heater bus metal 511 to heater bus metal 512 such that the power supply connected to connector structure 513 is able to supply power through heater bus metal 511 through the conductor cross-over 520 to heater bus metal 512 which provides the power to heating wire 510.

FIG. 6 illustrates one embodiment of a heater bus electrical cross-over from the iris layer to the patch layer within a border seal structure. Referring to FIG. 6, a conductive cross-over 620 is with the border seal 621 and provides an electrical connection between the heater bus metal 611 that is fabricated on the patch glass layer 601 to heater bus 612, which is on the iris glass layer 602. Heater wire 615 is fabricated on a portion of passivation layer 650 that is fabricated on top of iris metal 641 and is fabricated onto a portion of heater bus metal 612. In an alternative embodiment, there is a passivation layer between heater bus metal 612 and heating wire 615 with a via through the passivation layer connecting heater bus metal 612 and heating wire 615.

A patch overhang has no facing iris glass outside the border seal. An iris under hang has no facing patch glass outside the border seal. Metallization on an overhang or under hang is therefore accessible to make a connection to the heater power supply/controller. For example, this connection might be made by an ACF (anisotropic conductive adhesive) to a flex cable. This flex cable might connect to the heater power supply/controller. This heater power supply/controller might be on the aperture controller board or might be an independent power supply/controller unit.

Note that in the figures the patch glass, especially around the border seal region, has a number of other structures on it besides this heater wiring. The heater connection structures as drawn focus only on a method of supplying the heaters, and do not try to show the integration with other patch structures, for example, the voltage bus that connects from the patch overhang to the iris metal. A layer of passivation above the heater supply metallization 511 (in FIG. 5) and 611 (in FIG. 6), isolates this heater supply metallization from the rest of the patch circuitry.

Placement of the Heater Wiring, Heater Buses and Connections

The heater wiring and heater buses might be placed on either the patch glass side of the aperture, the iris glass side of the aperture, or have may have parts on both patch and iris glass (or non-glass) layers of the aperture. The connection for the heaters may come out on the patch glass layer or the iris glass layer side of the aperture.

Temperature Sensors Inside the RF Aperture

In one embodiment, one or more temperature sensors are located within the aperture. These temperature sensors are used to monitor the internal aperture temperature and to control whether the heater, including the heating elements (wires), heater buses and heater connections need to be engaged to regulate the temperature in the aperture. This may be necessary where the RF antenna elements need to be put in a certain temperature or range of temperatures. For example, when each of the RF antenna elements includes an LC, the antenna element operates more effectively if the LC is at a certain temperature. Therefore, by monitoring the temperature within the aperture and determining that the temperature of the LC is below its optimal temperature range, the heating wires, buses and connections can be used to heat the internal aperture until the LC is at the desired temperature range.

Using an Antenna Element Control Transistor (e.g., TFT) for Aperture Temperature Measurement

Embodiments of the invention include techniques for using a transistor (e.g., a TFT) integrated onto the patch layer substrate to measure LC temperature. In one embodiment, this technique uses the changing mobility characteristics of the TFT over temperature to indicate the temperature.

FIGS. 7A-7C are typical TFT Voltage vs Current curves at different temperatures. Referring to FIGS. 7A-7C, each chart has a plot for two values of Vds where the vertical axis is Id, the horizontal axis is Vgs.

Note that Id for a given Vds and Vgs changes over temperature. By using this TFT characteristic and setting the Vgs and Vds to known constant values, the measured Id value can be correlated to the temperature of the TFT.

FIG. 8A is a flow diagram of one embodiment of a process for determining an estimate of temperature of the LC using a TFT (or other type of transistor). The TFT is connected to the LC. Therefore, the temperature of the TFT provides an indication of the temperature of the LC. The process is performed by a temperature control system that includes a temperature monitoring subsystem.

Referring to FIG. 8A, the process begins by adjusting a digital voltage value, referred to as the digital-to-analog converter (DAC) value, until the voltage Vgs measurement analog-to-digital converter (ADC) indicates the predefined Vgs value (processing block 801). Next, processing logic in the temperature control system measures the current Id by reading the Id measurement ADC that is monitoring the voltage across a current sense resistor (processing block 802). Based on the Vgs voltage value and the Id current value, processing logic correlates the Id value to the calibrated temperature value (processing block 803). The correlation may be performed by a correlator/processing unit (e.g., processor) that access a lookup table (LUT) using the values to determine a corresponding temperature value for the TFT.

FIG. 8B illustrates an example of a temperature measurement circuitry. Referring to FIG. 8B, a voltage value is provided by DAC 861 to a circuit having current sensor resistor 862 coupled in series with a transistor 864. In one embodiment, a transistor 864 is in contact with liquid crystal (LC) in the RF antenna element. In one embodiment, transistor 864 comprises a thin film transistor (TFT). In one embodiment, the voltage value output from DAC 861 comes from a temperature controller 831. In one embodiment, a temperature adjustment unit 843 may provide different voltage values based on the type of transistor being monitored.

The voltage value across current sensor resistor 862 is monitored using comparator 863 to produce a current measurement that is converted to digital form by ADC 810. Based on the measurement current and the measured Vgs voltage, correlator 841 determines the temperature 842 of transistor 864 based on a correlation between transistor 864 and the measured current Id and Vgs voltage (processing block 803). Since transistor 864 is in contact with the LC, the temperature of transistor 864 is used to indicate or represent the temperature of the LC.

FIG. 8C is a flow diagram of one embodiment of a process for determining an estimate of temperature of the LC using a TFT (or other type of transistor) configured in a different manner than that of FIG. 8A. As in FIG. 8A, the TFT is connected to the LC and the temperature of the TFT provides an indication of the temperature of the LC. The process is performed by a temperature control system that includes a temperature monitoring subsystem.

Referring to FIG. 8C, the process begins by adjusting a digital voltage value, referred to as the digital-to-analog converter (DAC) value, until the voltage Vds measurement analog-to-digital converter (ADC) indicates the predefined Vds value (processing block 804). Next, processing logic in the temperature control system measures the current Id by reading the Id measurement ADC that is monitoring the voltage across a current sense resistor (processing block 805). Based on the Vds voltage value and the Id current value, processing logic correlates the Id value to the calibrated temperature value (processing block 806). The correlation may be performed by a correlator/processing unit (e.g., processor) that access a lookup table (LUT) using the values to determine a corresponding temperature value for the TFT.

FIG. 8D illustrates another example of a temperature monitoring circuit for a TFT using the procedure of FIG. 8C. The circuit in FIG. 8D is substantially similar to that of FIG. 8B with the exception that transistor 814 is coupled in a different way. Thus, the measuring by the monitoring subsystem and the operation of temperature controller 831 operates in the same way.

In one embodiment, multiple test TFTs can be distributed around the RF elements (and their LC) in the antenna array to measure the temperature at various locations and/or for temperature averaging.

Using Capacitance Properties of the LC to Measure LC Temperature

In one embodiment, LC temperature is measured by using the capacitance properties of the LC. This uses the characteristic of the LC that the electrical capacitance changes as a function of temperature.

In one embodiment, an electrical test capacitor is made by placing a conductive surface on the patch glass layer and a matching conductive surface be placed on the iris glass layer, thereby creating a capacitor with the LC acting as the separating dielectric material. These conductive surfaces are connected to circuitry that measures the capacitance (such as a capacitance-to-digital converter (CDC)). Since the capacitance of the LC is a function of temperature, the capacitance of the test capacitor can be correlated to the temperature of the LC directly.

FIG. 9 illustrates a circuit to determine the capacitance of the LC in order to determine the temperature of the LC in the RF antenna elements. Referring to FIG. 9, an excitation signal 901 is provided to a conductor 910D that connects iris glass layer 910E to liquid crystal 910C. In one embodiment, the excitation is a square wave. In one embodiment, the excitation signal 901 comes from a DAC with an input provided temperature controller 931. In one embodiment, a temperature adjustment unit 943 may provide different voltage values based on the type of test capacitor being monitored.

Patch glass layer 910A is coupled to liquid crystal 910C using conductor 910B. Applying the square wave of signal 901 to conductor 910D causes a capacitance to be created over liquid crystal 910C that is measured with Σ-Δ digital converter (CDC) 902. The output of CDC 902 is provided to temperature controller 931, which correlates the capacitance measurement, using correlator 941, to a temperature 942 of the LC of the LC-based test capacitor. This temperature is then used as the temperature of the LCs in the RF antenna elements in the array.

In yet another embodiment, the temperature monitoring subsystem is operable to measure decay speed of a liquid crystal and correlate the decay speed to a temperature of the liquid crystal. The decay speed of an LC is well-known in the art and the amount of time an LC is used is easily tracked. In one embodiment, the correlation operation is performed in the same manner as described above in conjunction with FIGS. 8B, 8D and 9.

In one embodiment, multiple test patches are distributed around the antenna array of RF LC-based antenna elements to measure the temperature various location and/or for temperature averaging.

The heater, including the heater elements and heater buses, is operated in conjunction with a temperature sensor to provide feedback to the heater system. The temperature sensor may be in the aperture or on the aperture. Some correlation of the temperature inside the aperture and the temperature measured by the sensor may need to be established by a calibration procedure.

In one embodiment, the temperature of the aperture is regulated by a control loop consisting of the temperature sensor and the heater power supply/controller. When the sensor indicates that the aperture is below its operational temperature, the heater power controller causes the heater to turn on to heat the aperture. There are many methods by which the desired aperture temperature can be controlled using the heater structures described herein.

In an alternative embodiment, instead of placing the heater inside of the RF aperture, the same types of heater wire patterns, heater wire pattern placement, heater buses and heater bus placements are made on a superstrate. In one embodiment, the superstrate is a substrate directly on the satellite facing side of the RF aperture. In one embodiment, the implementation is the same as is described above for use within the RF aperture (in the RF element/LC plane).

In one embodiment, when placing the heater on the superstrate, the superstrate is placed with the heater wire pattern between the top of the patch layer and the bottom of the superstrate, as close to the LC layer as possible. One potential problem with placing the heater on the superstrate is that the interaction of RF coming from the patch layer with the heater wires on the superstrate may have a detrimental effect on the RF pattern being formed by the RF aperture. To reduce the interaction of the RF with the heater wires, in one embodiment, the patch layer is thinned as much as possible, to move the heater as close to the RF element/LC plane as possible.

FIGS. 21A and 21B illustrate an example of a superstrate with a heater pattern attached thereto. Referring to FIGS. 21A and 21B superstrate 2101 includes a heater wire pattern 2103 on its bottom side. A heater bus 2102 is also attached to the bottom of superstrate 2101. Superstrate 2101 is coupled to segment 2100 that includes aperture area 2110 of RF antenna elements as shown in FIG. 21B, a patch overhang 2103.

Examples of Antenna Embodiments

The techniques described above may be used with flat panel antennas. Embodiments of such flat panel antennas are disclosed. The flat panel antennas include one or more arrays of antenna elements on an antenna aperture. In one embodiment, the antenna elements comprise liquid crystal cells. In one embodiment, the flat panel antenna is a cylindrically fed antenna that includes matrix drive circuitry to uniquely address and drive each of the antenna elements that are not placed in rows and columns. In one embodiment, the elements are placed in rings.

In one embodiment, the antenna aperture having the one or more arrays of antenna elements is comprised of multiple segments coupled together. When coupled together, the combination of the segments form closed concentric rings of antenna elements. In one embodiment, the concentric rings are concentric with respect to the antenna feed.

Overview of an Example of Antenna Systems

In one embodiment, the flat panel antenna is part of a metamaterial antenna system. Embodiments of a metamaterial antenna system for communications satellite earth stations are described. In one embodiment, the antenna system is a component or subsystem of a satellite earth station (ES) operating on a mobile platform (e.g., aeronautical, maritime, land, etc.) that operates using either Ka-band frequencies or Ku-band frequencies for civil commercial satellite communications. Note that embodiments of the antenna system also can be used in earth stations that are not on mobile platforms (e.g., fixed or transportable earth stations).

In one embodiment, the antenna system uses surface scattering metamaterial technology to form and steer transmit and receive beams through separate antennas. In one embodiment, the antenna systems are analog systems, in contrast to antenna systems that employ digital signal processing to electrically form and steer beams (such as phased array antennas).

In one embodiment, the antenna system is comprised of three functional subsystems: (1) a wave guiding structure consisting of a cylindrical wave feed architecture; (2) an array of wave scattering metamaterial unit cells that are part of antenna elements; and (3) a control structure to command formation of an adjustable radiation field (beam) from the metamaterial scattering elements using holographic principles.

Examples of Wave Guiding Structures

FIG. 10 illustrates an aperture having one or more arrays of antenna elements placed in concentric rings around an input feed of the cylindrically fed antenna. In one embodiment, the cylindrically fed antenna includes a coaxial feed that is used to provide a cylindrical wave feed. In one embodiment, the cylindrical wave feed architecture feeds the antenna from a central point with an excitation that spreads outward in a cylindrical manner from the feed point. That is, a cylindrically fed antenna creates an outward travelling concentric feed wave. Even so, the shape of the cylindrical feed antenna around the cylindrical feed can be circular, square or any shape. In another embodiment, a cylindrically fed antenna creates an inward travelling feed wave. In such a case, the feed wave most naturally comes from a circular structure.

Antenna Elements

In one embodiment, the antenna elements comprise a group of patch antennas. This group of patch antennas comprises an array of scattering metamaterial elements. In one embodiment, each scattering element in the antenna system is part of a unit cell that consists of a lower conductor, a dielectric substrate and an upper conductor that embeds a complementary electric inductive-capacitive resonator (“complementary electric LC” or “CELC”) that is etched in or deposited onto the upper conductor. As would be understood by those skilled in the art, LC in the context of CELC refers to inductance-capacitance, as opposed to liquid crystal.

In one embodiment, a liquid crystal (LC) is disposed in the gap around the scattering element. This LC is driven by the direct drive embodiments described above. In one embodiment, liquid crystal is encapsulated in each unit cell and separates the lower conductor associated with a slot from an upper conductor associated with its patch. Liquid crystal has a permittivity that is a function of the orientation of the molecules comprising the liquid crystal, and the orientation of the molecules (and thus the permittivity) can be controlled by adjusting the bias voltage across the liquid crystal. Using this property, in one embodiment, the liquid crystal integrates an on/off switch for the transmission of energy from the guided wave to the CELC. When switched on, the CELC emits an electromagnetic wave like an electrically small dipole antenna. Note that the teachings herein are not limited to having a liquid crystal that operates in a binary fashion with respect to energy transmission.

In one embodiment, the feed geometry of this antenna system allows the antenna elements to be positioned at forty five degree (45°) angles to the vector of the wave in the wave feed. Note that other positions may be used (e.g., at 40° angles). This position of the elements enables control of the free space wave received by or transmitted/radiated from the elements. In one embodiment, the antenna elements are arranged with an inter-element spacing that is less than a free-space wavelength of the operating frequency of the antenna. For example, if there are four scattering elements per wavelength, the elements in the 30 GHz transmit antenna will be approximately 2.5 mm (i.e., ¼th the 10 mm free-space wavelength of 30 GHz).

In one embodiment, the two sets of elements are perpendicular to each other and simultaneously have equal amplitude excitation if controlled to the same tuning state. Rotating them +/−45 degrees relative to the feed wave excitation achieves both desired features at once. Rotating one set 0 degrees and the other 90 degrees would achieve the perpendicular goal, but not the equal amplitude excitation goal. Note that 0 and 90 degrees may be used to achieve isolation when feeding the array of antenna elements in a single structure from two sides.

The amount of radiated power from each unit cell is controlled by applying a voltage to the patch (potential across the LC channel) using a controller. Traces to each patch are used to provide the voltage to the patch antenna. The voltage is used to tune or detune the capacitance and thus the resonance frequency of individual elements to effectuate beam forming. The voltage required is dependent on the liquid crystal mixture being used. The voltage tuning characteristic of liquid crystal mixtures is mainly described by a threshold voltage at which the liquid crystal starts to be affected by the voltage and the saturation voltage, above which an increase of the voltage does not cause major tuning in liquid crystal. These two characteristic parameters can change for different liquid crystal mixtures.

In one embodiment, as discussed above, a matrix drive is used to apply voltage to the patches in order to drive each cell separately from all the other cells without having a separate connection for each cell (direct drive). Because of the high density of elements, the matrix drive is an efficient way to address each cell individually.

In one embodiment, the control structure for the antenna system has 2 main components: the antenna array controller, which includes drive electronics, for the antenna system, is below the wave scattering structure, while the matrix drive switching array is interspersed throughout the radiating RF array in such a way as to not interfere with the radiation. In one embodiment, the drive electronics for the antenna system comprise commercial off-the shelf LCD controls used in commercial television appliances that adjust the bias voltage for each scattering element by adjusting the amplitude or duty cycle of an AC bias signal to that element.

In one embodiment, the antenna array controller also contains a microprocessor executing the software. The control structure may also incorporate sensors (e.g., a GPS receiver, a three axis compass, a 3-axis accelerometer, 3-axis gyro, 3-axis magnetometer, etc.) to provide location and orientation information to the processor. The location and orientation information may be provided to the processor by other systems in the earth station and/or may not be part of the antenna system.

More specifically, the antenna array controller controls which elements are turned off and those elements turned on and at which phase and amplitude level at the frequency of operation. The elements are selectively detuned for frequency operation by voltage application.

For transmission, a controller supplies an array of voltage signals to the RF patches to create a modulation, or control pattern. The control pattern causes the elements to be turned to different states. In one embodiment, multistate control is used in which various elements are turned on and off to varying levels, further approximating a sinusoidal control pattern, as opposed to a square wave (i.e., a sinusoid gray shade modulation pattern). In one embodiment, some elements radiate more strongly than others, rather than some elements radiate and some do not. Variable radiation is achieved by applying specific voltage levels, which adjusts the liquid crystal permittivity to varying amounts, thereby detuning elements variably and causing some elements to radiate more than others.

The generation of a focused beam by the metamaterial array of elements can be explained by the phenomenon of constructive and destructive interference. Individual electromagnetic waves sum up (constructive interference) if they have the same phase when they meet in free space and waves cancel each other (destructive interference) if they are in opposite phase when they meet in free space. If the slots in a slotted antenna are positioned so that each successive slot is positioned at a different distance from the excitation point of the guided wave, the scattered wave from that element will have a different phase than the scattered wave of the previous slot. If the slots are spaced one quarter of a guided wavelength apart, each slot will scatter a wave with a one fourth phase delay from the previous slot.

Using the array, the number of patterns of constructive and destructive interference that can be produced can be increased so that beams can be pointed theoretically in any direction plus or minus ninety degrees (90°) from the bore sight of the antenna array, using the principles of holography. Thus, by controlling which metamaterial unit cells are turned on or off (i.e., by changing the pattern of which cells are turned on and which cells are turned off), a different pattern of constructive and destructive interference can be produced, and the antenna can change the direction of the main beam. The time required to turn the unit cells on and off dictates the speed at which the beam can be switched from one location to another location.

In one embodiment, the antenna system produces one steerable beam for the uplink antenna and one steerable beam for the downlink antenna. In one embodiment, the antenna system uses metamaterial technology to receive beams and to decode signals from the satellite and to form transmit beams that are directed toward the satellite. In one embodiment, the antenna systems are analog systems, in contrast to antenna systems that employ digital signal processing to electrically form and steer beams (such as phased array antennas). In one embodiment, the antenna system is considered a “surface” antenna that is planar and relatively low profile, especially when compared to conventional satellite dish receivers.

FIG. 11 illustrates a perspective view of one row of antenna elements that includes a ground plane and a reconfigurable resonator layer. Reconfigurable resonator layer 1230 includes an array of tunable slots 1210. The array of tunable slots 1210 can be configured to point the antenna in a desired direction. Each of the tunable slots can be tuned/adjusted by varying a voltage across the liquid crystal.

Control module 1280 is coupled to reconfigurable resonator layer 1230 to modulate the array of tunable slots 1210 by varying the voltage across the liquid crystal in FIG. 11. Control module 1280 may include a Field Programmable Gate Array (“FPGA”), a microprocessor, a controller, System-on-a-Chip (SoC), or other processing logic. In one embodiment, control module 1280 includes logic circuitry (e.g., multiplexer) to drive the array of tunable slots 1210. In one embodiment, control module 1280 receives data that includes specifications for a holographic diffraction pattern to be driven onto the array of tunable slots 1210. The holographic diffraction patterns may be generated in response to a spatial relationship between the antenna and a satellite so that the holographic diffraction pattern steers the downlink beams (and uplink beam if the antenna system performs transmit) in the appropriate direction for communication. Although not drawn in each figure, a control module similar to control module 1280 may drive each array of tunable slots described in the figures of the disclosure.

Radio Frequency (“RF”) holography is also possible using analogous techniques where a desired RF beam can be generated when an RF reference beam encounters an RF holographic diffraction pattern. In the case of satellite communications, the reference beam is in the form of a feed wave, such as feed wave 1205 (approximately 20 GHz in some embodiments). To transform a feed wave into a radiated beam (either for transmitting or receiving purposes), an interference pattern is calculated between the desired RF beam (the object beam) and the feed wave (the reference beam). The interference pattern is driven onto the array of tunable slots 1210 as a diffraction pattern so that the feed wave is “steered” into the desired RF beam (having the desired shape and direction). In other words, the feed wave encountering the holographic diffraction pattern “reconstructs” the object beam, which is formed according to design requirements of the communication system. The holographic diffraction pattern contains the excitation of each element and is calculated by w_(hologram)=w_(in)*w_(out), with w_(in) as the wave equation in the waveguide and w_(out) the wave equation on the outgoing wave.

FIG. 12 illustrates one embodiment of a tunable resonator/slot 1210. Tunable slot 1210 includes an iris/slot 1212, a radiating patch 1211, and liquid crystal 1213 disposed between iris 1212 and patch 1211. In one embodiment, radiating patch 1211 is co-located with iris 1212.

FIG. 13 illustrates a cross section view of one embodiment of a physical antenna aperture. The antenna aperture includes ground plane 1245, and a metal layer 1236 within iris layer 1233, which is included in reconfigurable resonator layer 1230. In one embodiment, the antenna aperture of FIG. 13 includes a plurality of tunable resonator/slots 1210 of FIG. 12. Iris/slot 1212 is defined by openings in metal layer 1236. A feed wave, such as feed wave 1205 of FIG. 11, may have a microwave frequency compatible with satellite communication channels. The feed wave propagates between ground plane 1245 and resonator layer 1230.

Reconfigurable resonator layer 1230 also includes gasket layer 1232 and patch layer 1231. Gasket layer 1232 is disposed below patch layer 1231 and iris layer 1233. Note that in one embodiment, a spacer could replace gasket layer 1232. In one embodiment, iris layer 1233 is a printed circuit board (“PCB”) that includes a copper layer as metal layer 1236. In one embodiment, iris layer 1233 is glass. Iris layer 1233 may be other types of substrates.

Openings may be etched in the copper layer to form slots 1212. In one embodiment, iris layer 1233 is conductively coupled by a conductive bonding layer to another structure (e.g., a waveguide) in FIG. 13. Note that in an embodiment the iris layer is not conductively coupled by a conductive bonding layer and is instead interfaced with a non-conducting bonding layer.

Patch layer 1231 may also be a PCB that includes metal as radiating patches 1211. In one embodiment, gasket layer 1232 includes spacers 1239 that provide a mechanical standoff to define the dimension between metal layer 1236 and patch 1211. In one embodiment, the spacers are 75 microns, but other sizes may be used (e.g., 3-200 mm). As mentioned above, in one embodiment, the antenna aperture of FIG. 13 includes multiple tunable resonator/slots, such as tunable resonator/slot 1210 includes patch 1211, liquid crystal 1213, and iris 1212 of FIG. 12. The chamber for liquid crystal 1213 is defined by spacers 1239, iris layer 1233 and metal layer 1236. When the chamber is filled with liquid crystal, patch layer 1231 can be laminated onto spacers 1239 to seal liquid crystal within resonator layer 1230.

A voltage between patch layer 1231 and iris layer 1233 can be modulated to tune the liquid crystal in the gap between the patch and the slots (e.g., tunable resonator/slot 1210). Adjusting the voltage across liquid crystal 1213 varies the capacitance of a slot (e.g., tunable resonator/slot 1210). Accordingly, the reactance of a slot (e.g., tunable resonator/slot 1210) can be varied by changing the capacitance. Resonant frequency of slot 1210 also changes according to the equation f=1/2π√{square root over (LC)} where f is the resonant frequency of slot 1210 and L and C are the inductance and capacitance of slot 1210, respectively. The resonant frequency of slot 1210 affects the energy radiated from feed wave 1205 propagating through the waveguide. As an example, if fed wave 1205 is 20 GHz, the resonant frequency of a slot 1210 may be adjusted (by varying the capacitance) to 17 GHz so that the slot 1210 couples substantially no energy from feed wave 1205. Or, the resonant frequency of a slot 1210 may be adjusted to 20 GHz so that the slot 1210 couples energy from feed wave 1205 and radiates that energy into free space. Although the examples given are binary (fully radiating or not radiating at all), full gray scale control of the reactance, and therefore the resonant frequency of slot 1210 is possible with voltage variance over a multi-valued range. Hence, the energy radiated from each slot 1210 can be finely controlled so that detailed holographic diffraction patterns can be formed by the array of tunable slots.

In one embodiment, tunable slots in a row are spaced from each other by λ/5. Other spacings may be used. In one embodiment, each tunable slot in a row is spaced from the closest tunable slot in an adjacent row by λ/2, and, thus, commonly oriented tunable slots in different rows are spaced by λ/4, though other spacings are possible (e.g., λ/5, λ/6.3). In another embodiment, each tunable slot in a row is spaced from the closest tunable slot in an adjacent row by λ/3.

Embodiments use reconfigurable metamaterial technology, such as described in U.S. patent application Ser. No. 14/550,178, entitled “Dynamic Polarization and Coupling Control from a Steerable Cylindrically Fed Holographic Antenna”, filed Nov. 21, 2014 and U.S. patent application Ser. No. 14/610,502, entitled “Ridged Waveguide Feed Structures for Reconfigurable Antenna”, filed Jan. 30, 2015.

FIGS. 14A-D illustrate one embodiment of the different layers for creating the slotted array. The antenna array includes antenna elements that are positioned in rings, such as the example rings shown in FIG. 10. Note that in this example the antenna array has two different types of antenna elements that are used for two different types of frequency bands.

FIG. 14A illustrates a portion of the first iris board layer with locations corresponding to the slots. Referring to FIG. 14A, the circles are open areas/slots in the metallization in the bottom side of the iris substrate, and are for controlling the coupling of elements to the feed (the feed wave). Note that this layer is an optional layer and is not used in all designs. FIG. 14B illustrates a portion of the second iris board layer containing slots. FIG. 14C illustrates patches over a portion of the second iris board layer. FIG. 14D illustrates a top view of a portion of the slotted array.

FIG. 15 illustrates a side view of one embodiment of a cylindrically fed antenna structure. The antenna produces an inwardly travelling wave using a double layer feed structure (i.e., two layers of a feed structure). In one embodiment, the antenna includes a circular outer shape, though this is not required. That is, non-circular inward travelling structures can be used. In one embodiment, the antenna structure in FIG. 15 includes the coaxial feed of FIG. 9.

Referring to FIG. 15, a coaxial pin 1601 is used to excite the field on the lower level of the antenna. In one embodiment, coaxial pin 1601 is a 50Ω coax pin that is readily available. Coaxial pin 1601 is coupled (e.g., bolted) to the bottom of the antenna structure, which is conducting ground plane 1602.

Separate from conducting ground plane 1602 is interstitial conductor 1603, which is an internal conductor. In one embodiment, conducting ground plane 1602 and interstitial conductor 1603 are parallel to each other. In one embodiment, the distance between ground plane 1602 and interstitial conductor 1603 is 0.1-0.15″. In another embodiment, this distance may be λ/2, where λ is the wavelength of the travelling wave at the frequency of operation.

Ground plane 1602 is separated from interstitial conductor 1603 via a spacer 1604. In one embodiment, spacer 1604 is a foam or air-like spacer. In one embodiment, spacer 1604 comprises a plastic spacer.

On top of interstitial conductor 1603 is dielectric layer 1605. In one embodiment, dielectric layer 1605 is plastic. The purpose of dielectric layer 1605 is to slow the travelling wave relative to free space velocity. In one embodiment, dielectric layer 1605 slows the travelling wave by 30% relative to free space. In one embodiment, the range of indices of refraction that are suitable for beam forming are 1.2-1.8, where free space has by definition an index of refraction equal to 1. Other dielectric spacer materials, such as, for example, plastic, may be used to achieve this effect. Note that materials other than plastic may be used as long as they achieve the desired wave slowing effect. Alternatively, a material with distributed structures may be used as dielectric 1605, such as periodic sub-wavelength metallic structures that can be machined or lithographically defined, for example.

An RF-array 1606 is on top of dielectric 1605. In one embodiment, the distance between interstitial conductor 1603 and RF-array 1606 is 0.1-0.15″. In another embodiment, this distance may be λ_(eff)/2, where λ_(eff) is the effective wavelength in the medium at the design frequency.

The antenna includes sides 1607 and 1608. Sides 1607 and 1608 are angled to cause a travelling wave feed from coax pin 1601 to be propagated from the area below interstitial conductor 1603 (the spacer layer) to the area above interstitial conductor 1603 (the dielectric layer) via reflection. In one embodiment, the angle of sides 1607 and 1608 are at 45° angles. In an alternative embodiment, sides 1607 and 1608 could be replaced with a continuous radius to achieve the reflection. While FIG. 15 shows angled sides that have angle of 45 degrees, other angles that accomplish signal transmission from lower level feed to upper level feed may be used. That is, given that the effective wavelength in the lower feed will generally be different than in the upper feed, some deviation from the ideal 45° angles could be used to aid transmission from the lower to the upper feed level. For example, in another embodiment, the 45° angles are replaced with a single step. The steps on one end of the antenna go around the dielectric layer, interstitial the conductor, and the spacer layer. The same two steps are at the other ends of these layers.

In operation, when a feed wave is fed in from coaxial pin 1601, the wave travels outward concentrically oriented from coaxial pin 1601 in the area between ground plane 1602 and interstitial conductor 1603. The concentrically outgoing waves are reflected by sides 1607 and 1608 and travel inwardly in the area between interstitial conductor 1603 and RF array 1606. The reflection from the edge of the circular perimeter causes the wave to remain in phase (i.e., it is an in-phase reflection). The travelling wave is slowed by dielectric layer 1605. At this point, the travelling wave starts interacting and exciting with elements in RF array 1606 to obtain the desired scattering.

To terminate the travelling wave, a termination 1609 is included in the antenna at the geometric center of the antenna. In one embodiment, termination 1609 comprises a pin termination (e.g., a 50Ω pin). In another embodiment, termination 1609 comprises an RF absorber that terminates unused energy to prevent reflections of that unused energy back through the feed structure of the antenna. These could be used at the top of RF array 1606.

FIG. 16 illustrates another embodiment of the antenna system with an outgoing wave. Referring to FIG. 16, two ground planes 1610 and 1611 are substantially parallel to each other with a dielectric layer 1612 (e.g., a plastic layer, etc.) in between ground planes. RF absorbers 1619 (e.g., resistors) couple the two ground planes 1610 and 1611 together. A coaxial pin 1615 (e.g., 50Ω) feeds the antenna. An RF array 1616 is on top of dielectric layer 1612 and ground plane 1611.

In operation, a feed wave is fed through coaxial pin 1615 and travels concentrically outward and interacts with the elements of RF array 1616.

The cylindrical feed in both the antennas of FIGS. 15 and 16 improves the service angle of the antenna. Instead of a service angle of plus or minus forty five degrees azimuth (±45° Az) and plus or minus twenty five degrees elevation (±25° El), in one embodiment, the antenna system has a service angle of seventy five degrees (75°) from the bore sight in all directions. As with any beam forming antenna comprised of many individual radiators, the overall antenna gain is dependent on the gain of the constituent elements, which themselves are angle-dependent. When using common radiating elements, the overall antenna gain typically decreases as the beam is pointed further off bore sight. At 75 degrees off bore sight, significant gain degradation of about 6 dB is expected.

Embodiments of the antenna having a cylindrical feed solve one or more problems. These include dramatically simplifying the feed structure compared to antennas fed with a corporate divider network and therefore reducing total required antenna and antenna feed volume; decreasing sensitivity to manufacturing and control errors by maintaining high beam performance with coarser controls (extending all the way to simple binary control); giving a more advantageous side lobe pattern compared to rectilinear feeds because the cylindrically oriented feed waves result in spatially diverse side lobes in the far field; and allowing polarization to be dynamic, including allowing left-hand circular, right-hand circular, and linear polarizations, while not requiring a polarizer.

Array of Wave Scattering Elements

RF array 1606 of FIG. 15 and RF array 1616 of FIG. 16 include a wave scattering subsystem that includes a group of patch antennas (i.e., scatterers) that act as radiators. This group of patch antennas comprises an array of scattering metamaterial elements.

In one embodiment, each scattering element in the antenna system is part of a unit cell that consists of a lower conductor, a dielectric substrate and an upper conductor that embeds a complementary electric inductive-capacitive resonator (“complementary electric LC” or “CELC”) that is etched in or deposited onto the upper conductor.

In one embodiment, a liquid crystal (LC) is injected in the gap around the scattering element. Liquid crystal is encapsulated in each unit cell and separates the lower conductor associated with a slot from an upper conductor associated with its patch. Liquid crystal has a permittivity that is a function of the orientation of the molecules comprising the liquid crystal, and the orientation of the molecules (and thus the permittivity) can be controlled by adjusting the bias voltage across the liquid crystal. Using this property, the liquid crystal acts as an on/off switch for the transmission of energy from the guided wave to the CELC. When switched on, the CELC emits an electromagnetic wave like an electrically small dipole antenna.

Controlling the thickness of the LC increases the beam switching speed. A fifty percent (50%) reduction in the gap between the lower and the upper conductor (the thickness of the liquid crystal) results in a fourfold increase in speed. In another embodiment, the thickness of the liquid crystal results in a beam switching speed of approximately fourteen milliseconds (14 ms). In one embodiment, the LC is doped in a manner well-known in the art to improve responsiveness so that a seven millisecond (7 ms) requirement can be met.

The CELC element is responsive to a magnetic field that is applied parallel to the plane of the CELC element and perpendicular to the CELC gap complement. When a voltage is applied to the liquid crystal in the metamaterial scattering unit cell, the magnetic field component of the guided wave induces a magnetic excitation of the CELC, which, in turn, produces an electromagnetic wave in the same frequency as the guided wave.

The phase of the electromagnetic wave generated by a single CELC can be selected by the position of the CELC on the vector of the guided wave. Each cell generates a wave in phase with the guided wave parallel to the CELC. Because the CELCs are smaller than the wave length, the output wave has the same phase as the phase of the guided wave as it passes beneath the CELC.

In one embodiment, the cylindrical feed geometry of this antenna system allows the CELC elements to be positioned at forty five degree (45°) angles to the vector of the wave in the wave feed. This position of the elements enables control of the polarization of the free space wave generated from or received by the elements. In one embodiment, the CELCs are arranged with an inter-element spacing that is less than a free-space wavelength of the operating frequency of the antenna. For example, if there are four scattering elements per wavelength, the elements in the 30 GHz transmit antenna will be approximately 2.5 mm (i.e., ¼th the 10 mm free-space wavelength of 30 GHz).

In one embodiment, the CELCs are implemented with patch antennas that include a patch co-located over a slot with liquid crystal between the two. In this respect, the metamaterial antenna acts like a slotted (scattering) wave guide. With a slotted wave guide, the phase of the output wave depends on the location of the slot in relation to the guided wave.

Cell Placement

In one embodiment, the antenna elements are placed on the cylindrical feed antenna aperture in a way that allows for a systematic matrix drive circuit. The placement of the cells includes placement of the transistors for the matrix drive. FIG. 17 illustrates one embodiment of the placement of matrix drive circuitry with respect to antenna elements. Referring to FIG. 17, row controller 1701 is coupled to transistors 1711 and 1712, via row select signals Row1 and Row2, respectively, and column controller 1702 is coupled to transistors 1711 and 1712 via column select signal Column1. Transistor 1711 is also coupled to antenna element 1721 via connection to patch 1731, while transistor 1712 is coupled to antenna element 1722 via connection to patch 1732.

In an initial approach to realize matrix drive circuitry on the cylindrical feed antenna with unit cells placed in a non-regular grid, two steps are performed. In the first step, the cells are placed on concentric rings and each of the cells is connected to a transistor that is placed beside the cell and acts as a switch to drive each cell separately. In the second step, the matrix drive circuitry is built in order to connect every transistor with a unique address as the matrix drive approach requires. Because the matrix drive circuit is built by row and column traces (similar to LCDs) but the cells are placed on rings, there is no systematic way to assign a unique address to each transistor. This mapping problem results in very complex circuitry to cover all the transistors and leads to a significant increase in the number of physical traces to accomplish the routing. Because of the high density of cells, those traces disturb the RF performance of the antenna due to coupling effect. Also, due to the complexity of traces and high packing density, the routing of the traces cannot be accomplished by commercially available layout tools.

In one embodiment, the matrix drive circuitry is predefined before the cells and transistors are placed. This ensures a minimum number of traces that are necessary to drive all the cells, each with a unique address. This strategy reduces the complexity of the drive circuitry and simplifies the routing, which subsequently improves the RF performance of the antenna.

More specifically, in one approach, in the first step, the cells are placed on a regular rectangular grid composed of rows and columns that describe the unique address of each cell. In the second step, the cells are grouped and transformed to concentric circles while maintaining their address and connection to the rows and columns as defined in the first step. A goal of this transformation is not only to put the cells on rings but also to keep the distance between cells and the distance between rings constant over the entire aperture. In order to accomplish this goal, there are several ways to group the cells.

In one embodiment, a TFT package is used to enable placement and unique addressing in the matrix drive. FIG. 18 illustrates one embodiment of a TFT package. Referring to FIG. 18, a TFT and a hold capacitor 1803 is shown with input and output ports. There are two input ports connected to traces 1801 and two output ports connected to traces 1802 to connect the TFTs together using the rows and columns. In one embodiment, the row and column traces cross in 90° angles to reduce, and potentially minimize, the coupling between the row and column traces. In one embodiment, the row and column traces are on different layers.

An Example System Embodiment

In one embodiment, the combined antenna apertures are used in a television system that operates in conjunction with a set top box. For example, in the case of a dual reception antenna, satellite signals received by the antenna are provided to a set top box (e.g., a DirecTV receiver) of a television system. More specifically, the combined antenna operation is able to simultaneously receive RF signals at two different frequencies and/or polarizations. That is, one sub-array of elements is controlled to receive RF signals at one frequency and/or polarization, while another sub-array is controlled to receive signals at another, different frequency and/or polarization. These differences in frequency or polarization represent different channels being received by the television system. Similarly, the two antenna arrays can be controlled for two different beam positions to receive channels from two different locations (e.g., two different satellites) to simultaneously receive multiple channels.

FIG. 19 is a block diagram of one embodiment of a communication system that performs dual reception simultaneously in a television system. Referring to FIG. 19, antenna 1401 includes two spatially interleaved antenna apertures operable independently to perform dual reception simultaneously at different frequencies and/or polarizations as described above. Note that while only two spatially interleaved antenna operations are mentioned, the TV system may have more than two antenna apertures (e.g., 3, 4, 5, etc. antenna apertures).

In one embodiment, antenna 1401, including its two interleaved slotted arrays, is coupled to diplexer 1430. The coupling may include one or more feeding networks that receive the signals from elements of the two slotted arrays to produce two signals that are fed into diplexer 1430. In one embodiment, diplexer 1430 is a commercially available diplexer (e.g., model PB1081WA Ku-band sitcom diplexer from A1 Microwave).

Diplexer 1430 is coupled to a pair of low noise block down converters (LNBs) 1426 and 1427, which perform a noise filtering function, a down conversion function, and amplification in a manner well-known in the art. In one embodiment, LNBs 1426 and 1427 are in an out-door unit (ODU). In another embodiment, LNBs 1426 and 1427 are integrated into the antenna apparatus. LNBs 1426 and 1427 are coupled to a set top box 1402, which is coupled to television 1403.

Set top box 1402 includes a pair of analog-to-digital converters (ADCs) 1421 and 1422, which are coupled to LNBs 1426 and 1427, to convert the two signals output from diplexer 1430 into digital format.

Once converted to digital format, the signals are demodulated by demodulator 1423 and decoded by decoder 1424 to obtain the encoded data on the received waves. The decoded data is then sent to controller 1425, which sends it to television 1403.

Controller 1450 controls antenna 1401, including the interleaved slotted array elements of both antenna apertures on the single combined physical aperture.

An Example of a Full Duplex Communication System

In another embodiment, the combined antenna apertures are used in a full duplex communication system. FIG. 20 is a block diagram of another embodiment of a communication system having simultaneous transmit and receive paths. While only one transmit path and one receive path are shown, the communication system may include more than one transmit path and/or more than one receive path.

Referring to FIG. 20, antenna 1401 includes two spatially interleaved antenna arrays operable independently to transmit and receive simultaneously at different frequencies as described above. In one embodiment, antenna 1401 is coupled to diplexer 1445. The coupling may be by one or more feeding networks. In one embodiment, in the case of a radial feed antenna, diplexer 1445 combines the two signals and the connection between antenna 1401 and diplexer 1445 is a single broad-band feeding network that can carry both frequencies.

Diplexer 1445 is coupled to a low noise block down converter (LNBs) 1427, which performs a noise filtering function and a down conversion and amplification function in a manner well-known in the art. In one embodiment, LNB 1427 is in an out-door unit (ODU). In another embodiment, LNB 1427 is integrated into the antenna apparatus. LNB 1427 is coupled to a modem 1460, which is coupled to computing system 1440 (e.g., a computer system, modem, etc.).

Modem 1460 includes an analog-to-digital converter (ADC) 1422, which is coupled to LNB 1427, to convert the received signal output from diplexer 1445 into digital format. Once converted to digital format, the signal is demodulated by demodulator 1423 and decoded by decoder 1424 to obtain the encoded data on the received wave. The decoded data is then sent to controller 1425, which sends it to computing system 1440.

Modem 1460 also includes an encoder 1430 that encodes data to be transmitted from computing system 1440. The encoded data is modulated by modulator 1431 and then converted to analog by digital-to-analog converter (DAC) 1432. The analog signal is then filtered by a BUC (up-convert and high pass amplifier) 1433 and provided to one port of diplexer 1445. In one embodiment, BUC 1433 is in an out-door unit (ODU).

Diplexer 1445 operating in a manner well-known in the art provides the transmit signal to antenna 1401 for transmission.

Controller 1450 controls antenna 1401, including the two arrays of antenna elements on the single combined physical aperture.

Note that the full duplex communication system shown in FIG. 20 has a number of applications, including but not limited to, internet communication, vehicle communication (including software updating), etc.

Some portions of the detailed descriptions above are presented in terms of algorithms and symbolic representations of operations on data bits within a computer memory. These algorithmic descriptions and representations are the means used by those skilled in the data processing arts to most effectively convey the substance of their work to others skilled in the art. An algorithm is here, and generally, conceived to be a self-consistent sequence of steps leading to a desired result. The steps are those requiring physical manipulations of physical quantities. Usually, though not necessarily, these quantities take the form of electrical or magnetic signals capable of being stored, transferred, combined, compared, and otherwise manipulated. It has proven convenient at times, principally for reasons of common usage, to refer to these signals as bits, values, elements, symbols, characters, terms, numbers, or the like.

It should be borne in mind, however, that all of these and similar terms are to be associated with the appropriate physical quantities and are merely convenient labels applied to these quantities. Unless specifically stated otherwise as apparent from the following discussion, it is appreciated that throughout the description, discussions utilizing terms such as “processing” or “computing” or “calculating” or “determining” or “displaying” or the like, refer to the action and processes of a computer system, or similar electronic computing device, that manipulates and transforms data represented as physical (electronic) quantities within the computer system's registers and memories into other data similarly represented as physical quantities within the computer system memories or registers or other such information storage, transmission or display devices.

The present invention also relates to apparatus for performing the operations herein. This apparatus may be specially constructed for the required purposes, or it may comprise a general purpose computer selectively activated or reconfigured by a computer program stored in the computer. Such a computer program may be stored in a computer readable storage medium, such as, but is not limited to, any type of disk including floppy disks, optical disks, CD-ROMs, and magnetic-optical disks, read-only memories (ROMs), random access memories (RAMs), EPROMs, EEPROMs, magnetic or optical cards, or any type of media suitable for storing electronic instructions, and each coupled to a computer system bus.

The algorithms and displays presented herein are not inherently related to any particular computer or other apparatus. Various general purpose systems may be used with programs in accordance with the teachings herein, or it may prove convenient to construct more specialized apparatus to perform the required method steps. The required structure for a variety of these systems will appear from the description below. In addition, the present invention is not described with reference to any particular programming language. It will be appreciated that a variety of programming languages may be used to implement the teachings of the invention as described herein.

A machine-readable medium includes any mechanism for storing or transmitting information in a form readable by a machine (e.g., a computer). For example, a machine-readable medium includes read only memory (“ROM”); random access memory (“RAM”); magnetic disk storage media; optical storage media; flash memory devices; etc.

Whereas many alterations and modifications of the present invention will no doubt become apparent to a person of ordinary skill in the art after having read the foregoing description, it is to be understood that any particular embodiment shown and described by way of illustration is in no way intended to be considered limiting. Therefore, references to details of various embodiments are not intended to limit the scope of the claims which in themselves recite only those features regarded as essential to the invention. 

We claim:
 1. An antenna comprising: a physical antenna aperture having an array of radio frequency (RF) antenna elements formed with first and second substrates and a liquid crystal (LC) layer between the first and second substrates, the first substrate being an iris substrate; and a plurality of heating elements between the first and second substrates and interleaved between RF antenna elements in the array to heat the LC layer, each heating element integrated with iris elements as part of the iris layer on the iris substrate and contained within an area between a distinct pair of adjacently located RF elements in the array of RF elements.
 2. The antenna defined in claim 1 wherein heating elements in the plurality of heating elements are equidistant between RF antenna elements in the array.
 3. The antenna defined in claim 1 wherein heating elements in the plurality of heating elements are midway between rings of iris/patch antenna elements.
 4. The antenna defined in claim 1 wherein heating elements in the plurality of heating elements are in rings between the RF antenna elements.
 5. The antenna defined in claim 1 wherein the plurality of heating elements are wires.
 6. The antenna defined in claim 5 wherein a majority of the wires are of equal length with cross sections that are similar in dimension over the length of the heating wires.
 7. The antenna defined in claim 6 wherein the plurality of wires provides a same power dissipation per unit area over the antenna aperture.
 8. The antenna defined in claim 5 wherein heating wires are evenly distributed over the antenna aperture area.
 9. The antenna defined in claim 5 wherein width and height of a wire cross section of the heating wires varies over the antenna aperture while having a same power dissipation per unit area.
 10. The antenna defined in claim 5 further comprising heater power buses electrically connected to supply power to the heating wires, wherein one or more heater power buses are traverse through a border seal structure of the aperture.
 11. The antenna defined in claim 10 wherein the one or more heater power buses are electrically connected to a metal layer on an iris layer or a patch layer.
 12. The antenna defined in claim 1 further comprising a temperature monitoring subsystem to monitor temperature of RF antenna elements and control the plurality of heating elements to adjust the temperature of the RF antenna elements.
 13. The antenna defined in claim 12 wherein the temperature monitoring subsystem is operable to estimate a liquid crystal temperature of liquid crystal in the RF antenna elements.
 14. The antenna defined in claim 13 wherein the temperature monitoring subsystem comprises: one or more circuits comprising a voltage input, a current sense resistor and a transistor coupled in series wherein the transistor is integrated onto a patch layer in the antenna and in contact with liquid crystal; a temperature controller to provide an input voltage to the circuit; and a monitoring circuit to monitor voltage across the current sense resistor to obtain a measured current, wherein the temperature controller is operable to correlate the measured current to temperature of the transistor, the temperature of the transistor being indicative of the liquid crystal temperature.
 15. The antenna defined in claim 13 wherein the temperature monitoring subsystem is operable to measure the liquid crystal temperature by monitoring a voltage across a current sense resistor that is coupled in series with a transistor integrated onto a layer in the antenna and in contract with the liquid crystal, measuring the current through the current sense resistor, and correlating the current to the transistor temperature, the temperature of the transistor being indicative of the liquid crystal temperature.
 16. The antenna defined in claim 15 wherein the layer is a patch layer having a plurality of patches, wherein each of the patches is co-located over and separated from a slot in a plurality of slots, forming a patch/slot pair.
 17. The antenna defined in claim 13 wherein the temperature monitoring subsystem is operable to measure capacitance of a capacitor by matching conductive surfaces on the patch and iris layers in the aperture with liquid crystal therebetween, measuring capacitance of the capacitor with a circuit coupled to the conductive surfaces, and correlating the capacitance to temperature of the liquid crystal.
 18. The antenna defined in claim 13 wherein the temperature monitoring subsystem is operable to measure decay speed of a liquid crystal and correlate the decay speed to a temperature of the liquid crystal.
 19. The antenna defined in claim 1 wherein the heating elements are part of a heater wire pattern on a superstrate between the patch substrate and a bottom of the superstrate.
 20. The apparatus defined in claim 1 wherein the array of RF antenna elements comprises a tunable slotted array of antenna elements.
 21. The apparatus defined in claim 20 wherein the tunable slotted array comprises: a plurality of slots; a plurality of patches, wherein each of the patches is co-located over and separated from a slot in the plurality of slots, forming a patch/slot pair, each patch/slot pair being turned off or on based on application of a voltage to the patch in the pair; and a controller to apply a control pattern to control which patch/slot pairs are on and off to cause generation of a beam.
 22. An antenna comprising: a physical antenna aperture having an array of radio frequency (RF) antenna elements formed with first and second substrates and a liquid crystal (LC) layer between the first and second substrates, the first substrate being an iris substrate; a plurality of heating elements between the first and second substrates and interleaved between RF antenna elements in the array within the antenna aperture to heat the LC layer, each heating element of the plurality of heating elements integrated with iris elements as part of the iris layer on the iris substrate and contained within an area between a distinct pair of adjacently located RF elements in the array of RF elements; and a temperature monitoring subsystem to monitor temperature within the antenna aperture and control the plurality of heating elements to adjust the temperature of the RF antenna elements.
 23. The antenna defined in claim 22 wherein the temperature monitoring subsystem is operable to estimate a liquid crystal temperature of liquid crystal in the RF antenna elements.
 24. The antenna defined in claim 23 wherein the temperature monitoring subsystem comprises: one or more circuits comprising a voltage input, a current sense resistor and a transistor coupled in series wherein the transistor is integrated onto a patch layer in the antenna and in contact with liquid crystal; a temperature controller to provide an input voltage to the circuit; and a monitoring circuit to monitor voltage across the current sense resistor to obtain a measured current, wherein the temperature controller is operable to correlate the measured current to temperature of the transistor, the temperature of the transistor being indicative of the liquid crystal temperature.
 25. The antenna defined in claim 23 wherein the temperature monitoring subsystem is operable to measure the liquid crystal temperature by monitoring a voltage across a current sense resistor that is coupled in series with a transistor integrated onto a layer in the antenna and in contract with the liquid crystal, measuring the current through the current sense resister, and correlating the current to the transistor temperature, the temperature of the transistor being indicative of the liquid crystal temperature.
 26. The antenna defined in claim 25 wherein the layer is a patch layer having a plurality of patches, wherein each of the patches is co-located over and separated from a slot in a plurality of slots, forming a patch/slot pair.
 27. The antenna defined in claim 23 wherein the temperature monitoring subsystem is operable to measure capacitance of a capacitor by matching conductive surfaces on the patch and iris layers in the aperture with liquid crystal therebetween, measuring capacitance of the capacitor with a circuit coupled to the conductive surfaces, and correlating the capacitance to temperature of the liquid crystal.
 28. The antenna defined in claim 22 wherein the heating elements are part of a heater wire pattern on a superstrate between the patch substrate and a bottom of the superstrate.
 29. The apparatus defined in claim 22 wherein the array of RF antenna elements comprises a tunable slotted array of antenna elements.
 30. The apparatus defined in claim 29 wherein the tunable slotted array comprises: a plurality of slots; a plurality of patches, wherein each of the patches is co-located over and separated from a slot in the plurality of slots, forming a patch/slot pair, each patch/slot pair being turned off or on based on application of a voltage to the patch in the pair; and a controller to apply a control pattern to control which patch/slot pairs are on and off to cause generation of a beam. 